For any disease, it is a basic principle that an index representing the severity of its progression is required. In the treatment of periodontal disease as well as recent tooth implant treatment, the establishment of tooth extraction criteria with high predictivity is desired. Periodontal disease is a disease in which the alveolar bone supporting the teeth is disappearing. Upon complete disappearance of the alveolar bone, a denture inserted with the alveolar ridge as the base becomes unstable. Tooth implant procedure for implantation into the alveolar bone is also unfeasible, thus making it difficult to restore mastication.
At what point in time should a tooth with periodontal disease be judged unconservable? How should the diseased tooth be extracted based on this judgment, with a relatively large amount of the alveolar bone being retained? These are common problems in the treatment of periodontal disease. That is, presenting objective and unerring criteria for tooth extraction is an important, urgent matter.
SS/S (S=total periodontal membrane area, SS=remaining periodontal membrane area) has been studied since olden days by periodontists throughout the world as one of the diagnostic criteria for diagnosing periodontal disease, and methodologies for producing its values have been discussed variously. One of methods proposed for obtaining such diagnostic criteria comprises tracing an X-P photo on white paper, and measuring the amount of the alveolar bone surrounding the root of the tooth. Such a method, however, has not been successfully evaluated as presenting the same criteria, for causes such that it takes time because it has to trace X-P photos each time they are taken; the amount of X-P irradiation is not necessarily constant for all people; the direction of irradiation is not constant; and the bone densities of subjects are varied.
An improvement in these problems is a method which comprises taking pictures from a plurality of directions using computed tomography (CT) to reproduce three-dimensional periodontal tissue by use of a computer, thereby measuring SS/S. Periodontal disease screening generally done in periodontal treatment is performed dozens of times during a lifetime. In view of this fact, the above method utilizing CT gives an enormous amount of radiation exposure. Furthermore, this method is feasible as a method for experiments on a single subject such as human experimentation or animal experiments. However, under situations where most countries have only several CT devices/country, it is difficult to diagnose periodontal diseases on a wide scale by use of that method, except in an environment in which CT is in relatively widespread use. Besides, even if the SS/S could be accurately calculated, this index itself does not serve as a figure, which singly presents objective criteria, like other diagnostic methods such as the depth of a pocket. The above method involves the inconvenience that a diagnosis has to be made globally in consideration of results obtained by other diagnostic methods.
Patent Document 1 and Patent Document 2 are publicly known as prior art documents disclosing methods for examination of periodontal disease which comprise using a value, calculated as the ratio (SC/S) of the remaining root surface area (SC) supporting the current tooth to the total root surface area (S) supporting the healthy tooth, as a root surface area index, and examining the state of progression of periodontal disease based on this index.